Heretofore, audio encryption/decryption has been done on a per channel basis. Consequently, when a plurality of channels are used a corresponding plurality of encryption/decryption modules was required. Each of the encryption/decryption modules includes an integrated circuit chip set that implements the Data Encrytion Standard (DES) promulgated by the National Bureau of Standards as described in the "Data Encryption Standard", Federal Information Processing Standard (FIPS) Publication, No. 46, February, 1977. Thus, for a plurality of audio channels a corresponding plurality of the DES chip sets was required to perform decryption along with any associated apparatus.
Futhermore, in some encryption/decryption arrangements the decryptor must be synchronized with an associated encryptor. This synchronization is typically achieved by employing a separate synchronizing signal for each encryptor/decryptor pair. When using such synchronization signals in a digital system decoding of the signals is required which, in turn, requires additional apparatus for each channel.
Additionally, in certain systems it is desirable to perform checks on the encrytion/decryption and transmission processes for possible errors. This is usually realized by generating error control information prior to encrypting the audio signal which is transmitted separately for each of the channels. Then, the decryptor must regenerate the error control information and compare it to the transmitted error check information in order to detect any errors. Again, this is typically done on a per channel basis.
Consequently, all of these functions have required the use of duplicate apparatus for each channel which is costly and, therefore, undesirable.